Cancer starts when cells in the body begin to grow out of control. Cells in nearly any part of the body can become cancer, and can spread to other areas of the body. To learn more about how cancers start and spread, see What Is Cancer?
To understand esophagus cancer, it helps to know about the normal structure and function of the esophagus.
The esophagus is a hollow, muscular tube that connects the throat to the stomach. It lies behind the trachea (windpipe) and in front of the spine.
Food and liquids that are swallowed travel through the inside of the esophagus (called the lumen) to reach the stomach. In adults, the esophagus is usually between 10 and 13 inches long and is about ¾ of an inch across at its smallest point.
The wall of the esophagus has several layers. These layers are important for understanding where cancers in the esophagus tend to start and how they can grow.
Mucosa: This layer lines the inside of the esophagus. The mucosa has 3 parts:
- The epithelium forms the innermost lining of the esophagus and is normally made up of flat, thin cells called squamous cells. This is where most cancers of the esophagus start.
- The lamina propria is a thin layer of connective tissue right under the epithelium.
- The muscularis mucosa is a very thin layer of muscle under the lamina propria.
Submucosa: This is a layer of connective tissue just below the mucosa that contains blood vessels and nerves. In some parts of the esophagus, this layer also includes glands that secrete mucus.
Muscularis propria: This is a thick layer of muscle under the submucosa. It contracts in a coordinated, rhythmic way to push food along the esophagus from the throat to the stomach.
Adventitia: This is the outermost layer of the esophagus, which is formed by connective tissue.
The upper part of the esophagus has a special area of muscle at its beginning that relaxes to open the esophagus when it senses food or liquid coming toward it. This muscle is called the upper esophageal sphincter.
The lower part of the esophagus that connects to the stomach is called the gastroesophageal (GE) junction. A special area of muscle near the GE junction, called the lower esophageal sphincter, controls the movement of food from the esophagus into the stomach. Between meals, it closes to keep the stomach’s acid and digestive enzymes out of the esophagus.
Dysplasia is a pre-cancerous condition in which the cells lining the inside of the esophagus look abnormal when seen under a microscope. It is sometimes seen in people with a condition called Barrett’s esophagus, which is described in “What are the risk factors for cancer of the esophagus?”
Dysplasia is graded by how abnormal the cells look under the microscope. Low-grade dysplasia looks more like normal cells, while high-grade dysplasia is more abnormal and is linked to the highest risk of cancer.
Cancer of the esophagus (also referred to as esophageal cancer) starts in the inner layer (the mucosa) and grows outward (through the submucosa and the muscle layer). Since 2 types of cells can line the esophagus, there are 2 main types of esophageal cancer:
Squamous cell carcinoma
The esophagus is normally lined with squamous cells. Cancer starting in these cells is called squamous cell carcinoma. This type of cancer can occur anywhere along the esophagus. Once, squamous cell carcinoma was by far the more common type of esophageal cancer in the United States. This has changed over time, and now it makes up less than half of esophageal cancers in this country.
Cancers that start in gland cells are called adenocarcinomas. This type of cell is not normally part of the inner lining of the esophagus. Before an adenocarcinoma can develop, gland cells must replace an area of squamous cells, which is what happens in Barrett’s esophagus. This occurs mainly in the lower esophagus, which is where most adenocarcinomas start.
Adenocarcinomas that start at the area where the esophagus joins the stomach (the GE junction, which includes about the first 2 inches of the stomach called the cardia), tend to behave like cancers in the esophagus (and are treated like them, as well), so they are grouped with esophagus cancers.
Other types of cancer can also start in the esophagus, including lymphomas, melanomas, and sarcomas. But these cancers are rare and are not discussed further in this document.
Last Revised: 02/04/2016